Substantial Renovation - How to estimate costs

I am looking at a major renovation of a house in Sydney. I have engaged an architect as an initial sounding board and have done some initial look into what is are some possible improvements that will comply - (ie go up one story, add pool, new garage).

Whilst there are a few options on what can be done - I need to have a ball park estimate on the cost to see if it is feasible (on budget and future returns).

Whom can I get to estimate the construction costs of a few different options?
Ie - cost to add 2 rooms upstairs is approx $400k, or cost to dig in a new garage under the house $200k etc. I need to get quoted on a few options then can set a firm budget for my architect and make a realistic goal on the improvements.

Do you have plans? Quantity Surveyors like plans. A good architect will run their ideas past a QS and get a 'cost plan'. It won't be free, though. A QS will be reluctant to pluck figures out of the air based on a conversation about notional ideas. With the thought of 'two rooms upstairs', for example, there are a whole bunch of variables that could come into play. Within the existing roof line? If not, how much of the roof will be retained? What will the new roof be? Will the walls be light frame construction or brick? Bathroom upstairs? etc etc
Scott

Hi Scott, Thanks for your input. I have a rough schematic drawing from an architect. It shows one option only. I want to toss up this drawing with other possible renovations and compare which one is the best in terms of capital gains and cost. Once i know rough costs, i can get proper plans drawn up and costed up more accurately.

There are four stages of cost planning and it sounds like you could be in one or more of those stages. The aim of each stage is to provide the most accurate cost estimates with the information that is provided. The AIQS names of the stages and the estimates that they produce are:

Brief - indicative cost

Outline proposals - preliminary estimate

Sketch design - limit of cost estimate

Documentation - tender estimate

Cost planners use historical data form their own work as well as from price guides, such as Rawlinson's, which are compiled using thousands of jobs to find average values for individual project elements.

The brief design phase is used during the inception and feasibility stages and in your case would be a broad statement covering the option that you're looking at. It might be "Add two rooms above a Queenslander/brick house/etc." or "Add a basement garage to an existing house". With that information alone, a cost planner would be able to tell you the average price of the renovation based on the limited information that you have provided.

In the outline proposals phase there is generally more information available such as location, building type, floor areas, layouts and basic specifications. As this information is more specific they can use more specific price sources to provide a more accurate estimate. They can measure GFA, UCA and FECA and then apply historical rates to those values.

In addition to the information provided in the outline proposals phase, the sketch design phase contains the complete project brief, dimensioned sketch plans, elevation and section drawings, structural sketches with member dimensions, a schedule of finishes, site layout and specifications. With this information the cost planner can undertake an elemental costing. An example is where they calculate the amount of 3m high 90mm timber stud wall that is sheeted on both sides with 10mm plaster and painted with acrylic paint shown on your sketches. They then look up the cost for one metre and can estimate how much it will cost for your renovation. This is done for every individual element of the job.

The documentation stage sees the cost planner using the tender documents - plans and specifications - to check the work done in the sketch design phase and make any changes that are needed. At this time their role is also to advise the project team of any possible cost savings to the project.

At every stage, the provision of engineering information only improves the accuracy of the cost estimate. Also, locality indexes and inflation costs are applied to increase the accuracy of the estimate.

TLDR: It's slightly obvious (although I hate that word) but the more information you can provide allows for more accurate estimation of the costs.

Cost planners are usually estimators or quantity surveyors. I did a quick search for Sydney estimators and found this page. It has a couple of examples in the FAQ section which would be classed as the Documentation (Full Estimate) and Outline Proposals (Preliminary Estimate) stages.

While using a cost planner you should have a general idea of your budget and the profit that the project needs to make. If you engage a cost planner for a given stage and the project estimate is more than your budget you can use it as a guide to make decisions as to how to proceed.

@M-THIS
If you already have a schematic drawing, a chat with a few builders will also give you an idea of the cost range. As @Depreciator mentioned, there are no of variables. However I am assuming that the diagram will already define the no of bathroom, kitchen etc which typically tends to impact costing substantially. The other factor as mentioned is whether brick wall or not. I found chats with builders helped me learn a lot as well.

Can I ask how you went about finding/selecting an architect? I need to engage one.

@docplus - thanks for the suggestion. Re architect, I mainly called around to several architects that has many jobs in the council area and with similar build quality and style that i would like for my own property. From there, they explained more about their experience, fees etc.

Featured Business Member

Not all insurance is the same. Whether loss of rent due to a defaulting tenant, malicious or accidental damage or circumstances including tenant hardship and death of a tenant, EBM's RentCover insurance protects owners like no other policy.